1. Field of the Invention
This invention relates to a process for removing sulfur and heavy metals from a heavy crude oil by separating the crude oil into several fractions which are selectively hydrotreated, and are then recombined to form a synthetic crude oil of improved properties.
2. Description of the Prior Art
Christensen et al U.S. Pat. No. 3,902,991 discloses a process in which a reduced crude oil is vacuum fractionated into a vacuum gas oil and a vacuum residuum fraction. The vacuum gas oil fraction is then mildly hydrotreated to reduce the sulfur content thereof, while the vacuum residuum is more severely hydrotreated to also remove sulfur therefrom. Naphtha is taken off of both the hydrodesulfurization units (the vacuum gas oil unit and the vacuum residuum unit), and by combining a fraction derived from the hydrotreated vacuum residua with the product of desulfurization of the vacuum gas oil, a low sulfur fuel oil product is yielded.
The Christensen patent does not teach hydrodemetallation of either of the treated fractions, and does not propose to start with an untopped or unreduced heavy crude oil charge stock to yield, as a final product, a syncrude stream, the properties and characteristics of which can be tailored by the way in which the hydrotreating steps are carried out, all in accordance with the teachings of the present invention.
In Moritz U.S. Pat. No. 3,617,525, an atmospheric residuum is initially fractionated by vacuum distillation into a gas oil fraction and a heavy residuum fraction. The gas oil fraction is then desulfurized by hydrotreating, and the desulfurized gas oil is then recombined with the heavy residuum. The mixture of the previously desulfurized gas oil and the heavy residuum fraction is then subjected to hydrodesulfurization. The product is desulfurized residuum having a boiling point above about 650.degree. F.
The Moritz procedure is to be contrasted with that used in the present invention during which the heavy residuum from the initial fractionation of a heavy crude is hydrotreated to remove metals and sulfur, and in a parallel treating procedure, a distillate fraction (and optionally, a lighter naphtha fraction) is subjected (in parallel) to hydrodesulfurization. The desulfurized naphtha fraction and/or distillate fractions are then recombined with the hydrodemetallized heavy residuum to make a syncrude product.
In Gould U.S. Pat. No. 3,801,495, a procedure is disclosed in which crude oil is initially subjected to atmospheric distillation to yield atmospheric residuum and atmospheric gas oil. This gas oil is combined with gas oil produced by catalytically cracking a vacuum residuum produced upon vacuum distillation of the residuum from the atmospheric distillation. This vacuum distillation also yields a vacuum gas oil which is combined with the other gas oils. The mixture of gas oils is then subjected to hydrodesulfurization to yield a low sulfur content gas oil. The hydrogen employed for the hydrodesulfurization unit is produced by reforming methane.
There is no teaching in the Gould patent of hydrogen treating any of the heavy residuum streams, nor is there any disclosure of fractionating a crude oil charge stock into several fractions concurrently yielded by distillation, and then hydrotreating each of these fractions in parallel before recombining them to make a synthetic crude oil.
Fractionation of a sulfur-containing naphtha to provide a lower boiling fraction, an intermediate boiling fraction and a higher boiling fraction, each of which is then treated, by parallel treatment, to remove sulfur from the several fractions is taught in Howard et al U.S. Pat. No. 4,062,762. The desulfurized naphtha fractions are then combined in a blending zone. The higher boiling fraction withdrawn from the fractionator as the bottoms is subjected to hydrotreating to remove the sulfur therefrom. The intermediate fraction, however, is subjected to an alkali metal in combination with hydrogen to achieve desulfurization. The final blend which is achieved by this method is a low sulfur content naphtha.
The desulfurization procedures used in the process disclosed in the Howard et al patent for treating the intermediate and lower boiling fractions are not hydrotreating procedures as employed in the process of the present invention, and there is no teaching in the Howard et al patent of upgrading a heavy crude oil to a synthetic crude oil having customized properties.
In Bludis et al U.S. Pat. No. 4,022,683, a process is disclosed which has as its objective the hydrodenitrogenation of shale oil. The shale oil is initially fractionated into a relatively light fraction and a heavy fraction. These are then each subjected to a hydrotreating procedure in which a different catalyst is used for the hydrotreating of the light fraction as compared to the catalyst used in hydrotreating the heavy fraction. A principle objective, in the case of each hydrotreating procedure, is to remove nitrogen from the respective fraction treated, with a minimum of hydrocracking occurring. The effluent streams from each of the hydrotreating zones are blended after hydrotreating in which, the light fraction and heavy fraction are subjected to catalytic denitrogenation in the presence of hydrogen. The resultant composite stream is then fractionated to remove hydrogen sulfide, ammonia, naphtha and possibly a small amount of furnace oil as an overhead fraction.
The Bludis et al patent is silent as to any function of the hydrogen in removing sulfur from the shale oil, and there is no disclosure in this patent of the use of a heavy crude oil as the charge stock to the process, or of the development of a synthetic crude oil as the end product of the process.
In Frayer et al U.S. Pat. No. 3,876,530, a full crude oil is desulfurized in separate units. In one embodiment, a 650.degree. F.+ residuum containing metals in an excess quantity is hydrodesulfurized in a first unit, while a lighter distillate fraction is hydrodesulfurized separately in a second unit, and thus the problem of metal contamination and high catalyst deactivation is avoided with respect to at least the second unit. Thereupon the desulfurized distillate, or a portion thereof, and the desulfurized residua can be reblended to provide a total desulfurized crude oil.
Wilson U.S. Pat. No. 3,898,155 describes a process for simultaneously demetallizing and desulfurizing a heavy oil by employing a certain catalyst composition which has a controlled distribution of micropores and macropores so as to allow the catalyst to function effectively both for metal deposition thereon, and for desulfurization.
Rosinski et al U.S. Pat. No. 3,876,523 discloses a process for removing sulfur and certain deleterious metals, such as nickel and vanadium, from a petroleum crude oil by contacting the crude oil, in the presence of hydrogen, with an alumina base catalyst incorporating a Group VI-B metal and a Group VIII metal. A hydrogen pressure of from about 500 to about 3,000 p.s.i.g. is used, and the hydrogen circulation rate employed is from 1,000 to 15,000 s.c.f./bbl. The temperature used is from about 600.degree. F. to about 850.degree. F. and the space velocity is from about 0.1 to about 5.0 L.H.S.V. The demetallized and desulfurized oil thus produced can then be charged to a cracking zone or to a coking zone.